1. Field of the Invention
The invention generally relates to a process for use in purifying metallurgical grade silicon, and more particularly to a method of prepurifying metallurgical grade silicon through atmospheric control to remove a major portion of the impurities in producing silicon of a purity high enough for direct solar cell fabrication employing conventional Czochralski crystal growth processes.
2. Description of the Prior Art
Silicon solar cells, of course, are well known and have long been employed in celestial space environments. However, as is discussed in the instant inventor's prior U.S. Pat. No. 4,070,444, there recently has developed an increased interest in the use of photovoltaic silicon solar energy cells in the production of electrical energy for terrestrial uses. Unfortunately, the processes currently employed in obtaining silicon of a purity sufficient to fabricate such cells are relatively expensive, particularly in terms of the energy required in the production thereof.
Various attempts have been made to purify metallurgical grade silicon through chemical processes in which silicon halides are formed. For example, see U.S. Pat. Nos. 2,989,376 to Schaefer; 3,034,886 to Pruvot et al; and 4,070,444 to Ingle. However, the common approach has been simply to remove silicon from impurities.
It has been found possible to acquire a greater yield of silicon from metallurgical grade silicon, two or three times better than that obtainable when employing processes of the prior art, by removing impurities from the metallurgical grade silicon.
It is, therefore, the general purpose of the instant invention to provide an improved method for use in removing impurities from metallurgical grade silicon.